Process analysis systems:
It’s the little thing that count!
“Fizzy drinks - lemonade - pop: it’s all the same thing, isn’t it?”
By no means! It is the quality of the raw materials, the particular
composition of the recipe and the different manufacturing processes that make
the product what the customer wants: a desirable, stimulating, refreshing
drink. But if this result is to be achieved, the individual process steps must
be strictly observed during manufacture, in order to guarantee the quality of
the entire process.
Quality begins, of course, with the raw materials. Reception checks on
concentrates, essences etc. may require quite thorough analysis, which
generally can only be carried out using laboratory apparatus. It is advisable
to take a representative cross-sectional sample of the raw material.
If, for example, the raw material is milk, such a cross-sectional sample is
taken when the milk is pumped into the tank of the milk collecting truck at the
farm. The PS4 twin-headed sampler developed by GEA Diessel takes on the one
hand a representative sample of the milk supplied by the individual farm and at
the same time a sample of the entire content of the tank, i.e. of all the milk
collected on a round. This procedure ensures that all the milk is thoroughly
checked during transportation and right up to the time when it is discharged at
the processing facility. Not infrequently, a further sample of the tank content
is taken in the same way at the reception plant, thus providing a
cross-check.
The components that make up the milk, such as fat, protein and lactose, are
important for accounting and for planning the optimum further processing chain,
e.g. for drinking milk, cream, cheese etc. But it is even more important to
check for any possible substances that may represent a health hazard. EC
Directive no. 178/2002 requires that it should be possible to track foodstuffs
all the way from the producer to the marketable end product.
But even at an earlier date, the introduction of the ISO 9000 standard led
to the documentation of production steps with their processes and corresponding
demonstrations of quality taking root in the foodstuffs industry as a
fundamental business philosophy. Every step in the process is described in
detail, and the product that is going through the process is monitored at many
different points by a variety of devices. Laboratory technology is very
effectively supported by process measurement and analytic technology. These
procedures may be carried out INLINE, i.e. directly in the pipe through which
the product passes, or ONLINE, i.e. in a bypass pipe leading off from the main
pipe. This does away with the need for time-consuming sampling and sample
processing procedures, so that the results are available practically
instantaneously and can be reacted to immediately. For the most part, the
following parameters are measured at a great variety of different sampling
locations:
- Conductivity
- Density
- Refractive index
- Sound velocity
- Viscosity
- Turbidity
- Colour
- Percentages of dissolved CO2 and O2
- pH value
Raw material monitoring
Sugar, as the indispensable raw material in the manufacture of soft drinks,
is monitored for quantity and quality upon reception at the processing
facility, despite the inspections of outgoing goods that are mandatory at the
sugar factories. Only by using laboratory apparatus is it possible to determine
trace elements, e.g. the ash content, so that here again the sampling process
needs to be made as automated as possible.
The process-related metering of the concentration of the sugar solution
(whether the sugar was delivered in liquid form, or whether crystal sugar was
dissolved in a dissolution plant) takes place directly in the product pipe. The
physical measurement parameters - density, refractive index or sound velocity -
are particularly suitable for measurement in this way. Each of the individual
procedures can achieve a comparable degree of accuracy, which in the case of
sugar solution, for example, amounts to within 0.1 Brix. GEA Diessel can offer
volumetric metering of sugar solution with a type of apparatus approved by the
weights and measures authorities: a mass flow meter together with the
associated CS3 evaluation unit, with or without the determination of
concentration.
A technique that has become of ever greater interest is the monitoring of
the degree of inversion of the dissolved sugar. The period of time between the
dissolution of the sugar and its processing should be kept as short as
possible. The degree of inversion is therefore considered to be a parameter
demonstrating the “freshness” of the sugar base; it can be determined directly
in the product pipe by means of a combination of density and sound velocity
measurement (DI-Wave apparatus), since the velocity of sound in the sugar
solution alters very significantly as the saccharose breaks down into the
monosaccharides glucose and fructose.
Fruit syrup concentrates of apple, orange etc. are typically monitored for
their “Brix content” during the process. Especially if the initial product is
of a fibrous nature, the optical procedure of the refractometer is to be
recommended, since the measurement values are not falsified either by the
“pulp” content or even by small amounts of gas trapped in the product.
Every finished beverage consists of almost 90% water. The quality of this
raw material is thus extremely important, and must on no account be neglected.
Spring water gives a marked taste to the beverage. Although the specific
mineral composition can be monitored in the laboratory, it is practically
impossible to carry out a deliberate “post-mineralisation” of the water. On the
other hand, the production water is often demineralised in order to achieve a
consistent beverage quality.
Also important for the keeping properties and the taste of the finished
beverage is the oxygen content of the production water. GEA Diessel
manufactures equipment for the deaeration of water by a wide variety of
processes. Hot or cold deaeration, with or without the addition of CO2, can be
used, depending on the application, for soft drinks containing juice or carbon
dioxide or for beer based products. In order to monitor the degree of
effectiveness of, for example, a deaeration plant of the DI-OX type, the oxygen
content of the water is continuously measured and recorded as it emerges from
the water deaeration unit. In order to avoid batches that do not meet the
required standards, an alarm is triggered if the limit value of, say, 0.05 mg/l
oxygen content is exceeded.
Whereas in the past beverages were started “batchwise” in so-called
“syrup kitchens”, nowadays more and more INLINE mixing equipment is being used.
GEA Diessel’s DI-CON systems, which are equipped, for example, with the highly
accurate flow meters of the IZM series, are in service all over the world,
successfully mixing every imaginable product for the widest possible variety of
customers and in accordance with their very individual formulae.
In-line mixing unit of the “DI-CON” type, including carbonation
Purely by regulating proportions, this equipment can already achieve a very
high degree of accuracy. In order to identify faults in the metering equipment
as soon as possible, there is often the additional requirement for an immediate
analysis of the mixed product. It is important that the product should already
be well and homogeneously mixed before the analysis, i.e. downstream of the
mixing point there is, depending on the consistency of the product, a static or
even a dynamic blender. The time during which the analysis unit is addressed
must be correspondingly short. Pure two-component mixtures, e.g. juice
beverages consisting of fruit syrup and water, can be monitored very simply
during the process by the measurement techniques mentioned above.
In the case of multi-component mixtures (beverages containing sugar,
essence, concentrate, alcohol etc.), it may be necessary to select a
step-by-step analysis, or else a number of different measurement procedures
have to be applied (density, sound velocity, CO2 content measurement etc.),
which then require special mathematical analyses before useful results are
obtained.
In the soft drinks area, the finished beverage is typically held in a
buffer tank before the bottling equipment, and there a predetermined quantity
of carbon dioxide is added by the GEA Diessel CO2 injector in combination with
the DI-CAR measurement and control unit. A circulation pipe at the tank is used
for the continuous analysis of the Brix and CO2 content. The Brix measurement
is usually obtained using a density meter operating on the flexural resonator
principle, whilst the DI-Traco device uses the partial pressure and temperature
of the deaerated liquid sample to determine the proportion of dissolved CO2 by
Henry-Dalton’s Law. In order to be able to fulfil the exacting requirements for
accuracy that the finished beverage has to comply with, the measurement values
determined in this way are used to fine-tune the product in the regulating loop
of the mixing apparatus.
“DI-CAR” carbonation station for soft drinks, with analysis units for
Brix and CO2
The purely physical metering procedures described are generally not able to
determine the individual ingredients “directly”, i.e. specifically. That is to
say: when density, sound velocity etc. are measured, these are always “combined
value parameters”, through which it is only possible to calculate the
concentration indirectly. Spectral procedures, on the other hand, such as
infrared measurement techniques in the near (NIR) or middle (MIR) spectral
range provide far more information on the (molecular) structure of the product
to be investigated. The component ingredients of milk, for example, such as
fat, protein and lactose, can only be determined by an MIR measuring system.
In process measurement technology, these “true” analysis procedures are
still in their infancy. The acid content of a beverage, for example, can also
only be determined indirectly by measuring the conductivity or the pH value.
For beer, as a multi-component mixture of water, extract, alcohol and dissolved
CO2, the sonic measuring technique became established more than 20 years ago as
a very practical method of determining the original gravity.
This is thanks to the particular behaviour of sound during the fermentation
of sugar to alcohol. Whereas density is sharply reduced by the alcohol
produced, the sound velocity only alters very little. Thus original gravity can
be calculated very simply and with a good degree of precision. The measuring
head is wear and maintenance free, and is made completely of stainless steel,
so that in its robust construction it displays all the characteristics of an
ideal process measurement system.
This simple and effective measuring device is installed directly in the
product pipe using a VARIVENT housing, so that the installation is perfectly
hygienic and does not lead to any bacteriological risk to the beverage.
The DI-Check measuring system developed and manufactured by GEA
Diessel offers all the signals required for process control. The integrated
temperature measurement supplies a measurement value with compensation within a
range of some 8-10 degrees. If the slight influences of the proportion of
alcohol to extract or of the dissolved CO2 are also to be compensated for, the
measurement system can be expanded by the addition of density and CO2 measuring
functions (the DI-Wave device). In continuous beer mixing apparatus (“original
gravity optimisation plant”) these measurement signals serve for the fine
tuning of the finished beverage with regard to its original gravity or alcohol
content.
Product monitoring and quality control
Bottling or filling is normally the last production step, giving rise to the
feeling that “Nothing more can go wrong now!” But it may happen that wrongly
switched valves lead either to the bottle, can, etc. being filled with
completely the wrong product, or else that leakages give rise to a change in
the nature of the beverage even at this late stage. And it is at this stage
that the value of the product is at its maximum: your company’s image is at
stake, and you may face enormous claims for compensation. Product monitoring
will provide security, and at the same time the complete documentation will
provide the necessary evidence of quality assurance in the facility. In the
most simple case, the measurement systems already described are used again. For
example, combination with an IZM flow meter will provide not only time-based
but also volume-based records.
GEA Diessel’s DI-Liquiz and DI-Lab apparatus generate a batch log for every
batch, which is easy to print out or can be transferred to a computer, e.g.
using a Profibus interface, as a data record. It is of course also possible to
visualise all measurement values on the computer.
It is also possible to integrate a counting function for the number of
packages filled, and so to compare plan and actual quantities and thus provide
information “on-line” about the efficiency of the filling equipment. Lost
quantities are identified at an early stage, so that corrective measures can be
implemented quickly.
While the DI-Liquiz combined measurement system is designed specially for
determining volumes and original gravities of beer, the modular DI-Lab system
allows a variety of production parameters to be adapted for use in continuous
monitoring and documentation. Measuring devices for conductivity, colour,
turbidity, concentration etc. can also be connected to the data recording
system at a later date.
Automated cleaning
The effectiveness of cleaning can be monitored through the process
parameters of flow speed, temperature, concentration of the cleaning medium and
duration of the cleaning process. This data is also integrated, e.g. in GEA
Diessel’s DI-CIP apparatus.
Summary
INLINE and ONLINE process analysis technology effectively supports the
quality and effectiveness of the beverage manufacturing process at the vital
points. Even though the typical physical measurement techniques do not offer
any high level of specificity, they have proved themselves outstandingly in
many facilities on account of the simplicity with which they can be installed
and calibrated for familiar applications, and because of their largely wear and
maintenance free design. Efficiency is often enhanced to such an extent, e.g.
through the optimisation of the use of raw materials, that the capital costs
are rapidly amortised. GEA Diessel supplies either individual devices, combined
measurement systems or complete product lines and plants.
The author:
Hermann Hartmann. Dipl.Phys., responsible for measurement
and data technology at GEA Diessel